Cylinder Ring

HOERBIGER Compression TechnologyHOERBIGER Compression Technology

Cylinder Rings

General Understanding

Cylinder Rings

General Understanding

Cylinder rings

Piston rings : between Piston and cylinder liner,

seal the compression space

Rider rings : Carry the weight of the piston and

half of the rod but should not seal

Basic Understanding

Manufacturing of Rings at HRP

6.1.2

for differential pressures 0.1 to 400 bar

for piston diameters 20 to 1400 mm

made of metals cast iron, bronze

and non metallics filled PTFE, PEEK, PPS, Carbon

Cylinder

Rings

Cylinder Rings

Nomenclature of Dimensions

LinerLiner

PistonPiston

axial clearance

axial clearance

axialring width .

axial riderring width

width of rider

ring groovewidth of piston

ring groove

cylinder DIA

outer DIA

of piston

inner DIA of

piston ring

piston ring

groove DIA

rider ring

grooveDIA

inner DIA of

rider ring

running

clearance

rider ring

radial thickness

piston ring

radial thickness

6.6.1

18/04/2012 5

Cylinder Ring Design Selection – Main Factors

The main factors which influence the design selection are:

• Pressures -> number of rings, style, material

• Temperature -> material, type, ring sizes

• Gas, its mol weight and state (lube, wet, dry, bone dry) -> number of rings

material, style

• Cylinder, Piston and Rod design -> size, style

• The allowable dimensions for our components -> number of rings, size, style

• Required features (pin hole, pressure balancing or reliving) -> ring style

• Counterface of the cylinder / liner or piston rod -> material

Basic Understanding

Number of Rings According to Experience

6.2.6

Differential Pressure Recommended Number

bar gauge psig of PTFE-Rings per Piston

0 - 10 0 - 150 2

10 - 15 150 - 225 3

15 - 25 225 - 375 4

25 - 30 375 - 450 5

30 - 50 450 - 750 6

50 - 100 750 - 1500 7

100 - 200 1500 - 3000 8

200 - 320 3000 - 4725 9

320 - 400 4725 - 6000 10

Differential pressure for

single acting compressors : Outlet pressure minus atmospheric pressure

double acting compressors: Outlet pressure minus inlet pressure

18/04/2012 7

Cylinder Rings – Over Run IssueThe piston rings must not leave the sliding area

UCL = Piston ring stack length + piston stroke - 2 x over-run

Bearing surface

Ring stack length

Sliding area = uninterupted

cylinder length (UCL)

Over-run < 3 mm or

< 25 % of ring width

Detail:

8

Basic Understanding

Ring Styles

pressure

balanced

with

expander

without

expander

twin

ring

6.2.3

Cut

Ring Profiles

straight cut angle cut overlapped cut

or step cut

Basic Understanding

Increasing Sealing Ability

6.2.4

Cut Rings with expander

Twin Piston Ring

single acting:

Cut rings, pegged together.

Rings for low pressure

applications,large diameters

Sealing is improved

by springing the ring

to the liner.

Double Twin

Piston Ring:

The smaller ring

blocks the gap in

the L-shaped ring

in one direction

Double twin

piston rings

seal in both

directions.

6.2.5

Basic Understanding

Pressure Compensation

Piston ring designs for high pressure application:

without pressure balancing with pressure balancing

force profile torsionforce profile torsion

unbalanced

force

unbalanced

force

Piston rings without pressure balancing will wear quick at high

differential pressures due to high contact pressure between the piston

ring and the liner. Grooves and radial holes of pressure balanced rings

allow a controlled leakage to the outer ring diameter; thereby reducing

the unbalanced force and torsion moment promoting reduced wear.

11

Description:

Simplest ring with

rectangular section

and straight cut (gap).

• Ring will not spin,

therefore preferred on

soft aluminium piston

Application:

Standard piston ring.

Standard Piston Ring Types

Ring Type 0800

straight cut

6.3.1

12

Description:

Ring with rectangular section

and angle cut.

• Greater sealing efficiency created by longer leakage

path for gas due to angle cut.

• Ring gap will not form witness lines on the cylinder liner.

Application:

Standard piston ring for

non brittle materials.


Ring Type 0801

angle cut

6.3.2

13

Description:

Ring with rectangular

section and angle cut,

2 piece design.

Application:

For smaller ring diameters

and less flexible materials,

to mount without warming up.


Ring Type 0804

angle cut

6.3.3

14

Description:


and step cut, greater sealing

efficiency created by smaller

gaps, more expensive.

Application:

Piston ring for greater sealing

efficiency.

Not for brittle materials!


Ring Type 0808

step cut,

(overlapped gap)

6.3.4

15

Description:


and step cut, 3 piece design,

greater sealing efficiency

created by smaller gaps,

more expensive.

Application:

For smaller ring diameters

and less flexible materials,

(especially metallic rings,

e.g. Bronze).


Ring Type 0811

step cut

(overlapped gap)

6.3.5

16

Description:

Pressure balanced ring with

rectangular section and angle cut.

Less pressure load but approx.

the same cross sectional area.

Application:

For high differential pressure per

ring. Longer life than plain rings.


Pressure Balanced Ring Type 0803

6.3.6

angle cut

17

Description:

Pressure balanced ring with

rectangular section and angle

cut, 2-piece design.

Less pressure load but approx.

the same cross sectional area.

Application:

For high differential pressure

per ring, longer life than plain

rings. For non-flexible materials.


Pressure Balanced Ring Type 0805

6.3.7

angle cut

18

Description:

Twin ring consisting of an

L-ring and a rectangular ring

both straight cut and pegged

together so that the gap of the

rectangular ring is covered

by the L-ring.

rectangular ring

L-ring

Application:

The Twin Piston Ring is single

acting and only seals against

the small rectangular ring.

For light gases.


Twin Piston Ring Type 0820

6.3.8

L-ring rectangular ring

gap

gap

19

Description:

Double Twin Ring consisting

of a T-ring type 0816 and

2 rectangular rings all straight

cut and pegged together so

that the gaps of the rectangular

rings are covered by the T-ring.

rectangular rings

T-ring type 0816

Application:

Double Twin Rings seal

in both directions.


T-Section Double Twin Ring Type 0816

6.3.9

T-ring T-ring Rectangular ringsRectangular rings

20Basic UnderstandingBasic Understanding Ring TypesRing Types

6.4

Rider RingsRider Ringsfor Compressors

18/04/2012 21

Rider Rings - BasicsFunctions of Rider Ring is to:

• support the piston

• prevent it from contacting the liner.

The Rider Ring should not seal the gas ! • specific bearing load

• ring projection

• piston velocity

• liner surface quality

• liner cooling

• gas type

• gas condition

• bedding in procedure

Factors which influence

Rider Ring wear:

22

Task:– to prevent the piston from contacting the cylinder liner.

– the rider ring should not seal the gas.

Design Criteria:– bearing load

– piston and liner material

– hardness of the liner

– surface quality of the liner

– lube or non lube

– gas type

Specific load values:– lube 0,07 MPa

– non lube 0,035 MPa

Calculation of load:

=weight of the piston* + half the rod weight*OD of rider ring x width of all rider rings

Basic Understanding

Task - Calculation

width of rider ring

OD

6.4.1

* for V- and W-form compressors only the component of weight vertical to the liner

Basic Understanding

Axial Clearance

6.4.3

Correct design of axial clearance

is important for good operation

The ring moves backwards and

forwards in the piston groove

hitting both groove side faces

causing the ring and the groove

side faces to be damaged.

Ring is deformed so that it

bellows within the groove.

axial clearance is too great

axial clearance is too small

axial clearance

Documents

Cylinder Ring